Director Robert Eggers’ revenge epic The Northman has been called the “definitive Viking film,” but, funnily enough, no one in the movie ever says the word “Viking.” For archaeology professor Neil Price, one of three historical consultants who worked on The Northman, that felt like a win. “Not everybody who lived in the Viking Age was a Viking,” Price, the author of Children of Ash and Elm: A History of the Vikings, a definitive account of the Viking Age, told TIME. “The people of this time were individuals, every bit as complicated and varied as we are. This film will hopefully push people to think differently about the Vikings beyond the usual clichés.”

It’s true: The Northman, in theaters April 22, is not your usual horned helmet fare. The film, primarily set in 10th-century Iceland, tells the story of Prince Amleth (Alexander Skarsgård), a royal-turned-warrior who goes on a bloody, mystical journey to avenge the murder of his father (played by Ethan Hawke). Thanks to Eggers’s previous films, 2016’s The Witch, set in 1690 New England, and 2019’s The Lighthouse, which takes place on a mysterious New England island in the 1890s, the director has earned a reputation for paying close attention to historical detail. (“He really does an enormous amount of background research. I sometimes wonder whether he needs advisors,” Price joked.) With The Northman, Eggers hit a new level in his quest for historical truth, striving to perfect even the smallest details in the film, which he co-wrote with Icelandic novelist and poet Sjón. “Let’s be clear,” Price said. “There are limits to what historians know about that time. It’s a thousand years ago, so there are gaps.”

Filling in the gaps was part of the fun for Price, who sent Eggers and the film’s crew “hundreds of images of clothes, buildings, weapons” to help them during pre-production. When he visited the Belfast set in March 2020, right before the film went on hiatus due to COVID-19, Price said he was “overwhelmed” by the world Eggers had created. “It feels complete and layered, but it’s a world that has different values than ours, different assumptions, different beliefs, different concepts of reality,” he said. “It is different from our reality and it’s quite frightening, but you can see something of yourself in it somewhere—if you want to.” Below, Price offers historical context for The Northman.

In The Northman, a young prince named Amleth seeks revenge on his uncle Fjölnir (played by Claes Bang) for killing his father and then marrying his mother, Queen Gudrún (Nicole Kidman). That plot might sound familiar to anyone who’s read Shakespeare. Hamlet was actually inspired by the story of Amleth, which was a small section of a larger saga written in the early 13th century by a Danish historian named Saxo. “The assumption is that [the story of Amleth is] based on something very old, certainly in the Viking Age,” Price said. “And might even be older than that.”

Eggers decided to set Amleth’s story in the Viking Age. He also decided to add a few twists to the original saga to make it his own. “It’s a film where you recalibrate what is going on as you’re seeing it,” Price said. “Then you realize what you saw before is not quite what you thought it was—or at least, not what Amleth thought it was.”

The first time the audience meets adult Amleth (Skarsgård), he’s gone from little prince to berserker, a brutal warrior who is more beast than man. Price admits there’s a divide between academics on whether the berserkers really existed or not. Some say the berserkers are merely characters in Icelandic sagas and medieval literature, while others believe they were basically Viking special forces. There are even those who think there was a supernatural element to the rituals the berserkers reportedly performed before battle. “We know that during the Viking Age, there were very clear beliefs in shape-shifting. The idea of men switching physically into animals, big predators like wolves and bears,” Price explained. “We have metal figures that depict basically naked men wearing skins and holding spears. They appear to be dancing.”

In stories from the Viking Age, the berserkers are described as running into battle without armor, convinced iron could not hurt them. “There are some descriptions of Vikings in combat, written by the people who they were fighting, who talk about them making noises like animals and moving like animals,” Price said. Eggers wanted to bring those descriptions of men howling like predators to life in The Northman. “Robert lets you see how Amleth’s rage just absolutely consumes him,” Price said. “Then you see what he does with it.”